This research plan proposes studies of the hormonal regulation of the growth and function of clonal, hormonally responsive osteoblast-like cells, both normal and neoplastic. The specific aims are to characterize the metabolic requirements and effects of known hormones on growth of these cells, to evaluate the role of some intracellular growth regulating lipids with studies in mevalonic acid and arachidonic acid metabolism, and to study the effect of other hormones on expression of PTH-responsive adenylate cyclase in serum-free culture. Studies will be conducted using rat and human osteogenic sarcoma cell lines and normal newborn rat bone cells, with rat fibroblasts as control cells. The basis for all of these studies is the discovery in our laboratory of an important role for lipids (low density lipoproteins) in the growth of osteoblast-like cells. We have used these observations on lipoproteins to develop a serum-free culture system for the study of hormonal control of osteoblast-like cell function. The effects of nutrients, calcitropic hormones, other hormones, and growth factors on cell growth will be assessed by cell number and/or protein and DNA. Assays for 3-hydroxy-3-methylglutaryl coenzyme A reductase and arachidonic acid release will be used for studies of hormonal regulation of lipid metabolism. The expression of adenylate cyclase in serum-free culture will be assessed by both cell cAMP accumulation and membrane adenylate cyclase assays. The long-term objectives of this proposal are to develop observations and models of osteoblast proliferation which can be tested in more complex bone systems, in order to understand the role of bone cell proliferation in the integration of bone physiology and in metabolic bone disease.